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J.L. Demer, E.C. Engle; Magnetic Resonance Imaging (MRI) Demonstrates the Endophenotype of Duane’s Radial Ray (Okihiro) Syndrome (DRRS) . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2353.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We employed high resolution, multipositional MRI to demonstrate directly the extraocular muscles (EOMs) and associated motor nn. in hereditary DRRS, a form of Duane retraction syndrome (DRS) due to mutations in the transcription factor SALL4. Methods: We enrolled 4 male and 2 female affected members of an autosomal dominant DRRS pedigree co–segregating a heterozygous SALL4 mutation. Coronal T1 weighted MRI scans of the orbits were obtained using surface coils in multiple gaze positions at 2 mm thickness (234–312 micron resolution), as well as oblique heavily T2 weighted images in the plane of the cranial nn. at 1 mm thickness (390 micron resolution). MRI findings were correlated with motility examinations, and compared with similar images in 9 normal volunteers. Results: Most but not all subjects with DRRS had radial ray abnormalities including thumb, radial artery, radial bone, and pectoral muscle hypoplasia. Two had unilateral and 4 bilateral ocular involvement. Six eyes had limitation of both ab– and adduction, two eyes had limitation only of abduction, and one eye had limitation only of adduction. Affected eyes had typical lid fissure narrowing and retraction in adduction. One subject had bilaterally limited supraduction. Three subjects had esotropia and one had V pattern exotropia. Intraorbital and intracranial abducens nn. (n6) were small to absent, most severely ipsilateral to abduction deficiency. All cases had normal intracranial oculomotor nn (n3). Optic n. (ON) cross section was reduced by 37% compared with control (P<0.0002), but visual acuities were normal. EOMs were structurally normal in all but one case who had bilateral abnormality of the deep LR. In one eye the LR pulley slipped inferiorly in adduction, and in 2 eyes the rectus pulley array was extorted bilaterally. In affected orbits, a branch of n3 closely approximated and presumably innervated the LR. Conclusions: DRRS has a variable and asymmetric phenotype including all 3 forms of Duane syndrome. The endophenotype of DRRS includes marked n6 hypoplasia, but not the widespread EOM structural abnormalities and n3 hypoplasia typical of dominant DRS linked to chromosome 2. In DRRS, the LR may be innervated or co–innervated by n3. The presence of ON hypoplasia suggests that SALL4 is not limited to motor nn, but is also involved with ON development. Pulleys are only occasionally heterotopic or unstable in DRRS, suggesting that these may be secondary mechanical effects of chronic EOM co–contraction.
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